Electric heater



C. C. ABBOTT ELECTRIC HEATER July 15, 1930.

Filed May 17, 1929 Ice Charles 0 Abbott, b WM 9 His Attorney.

Patented July 15, 1930 UNITED STATES PATENT OFFICE CHARLES C. ABBOTT, OFPITTSFIELD, MASSACHUSETTS, ASSIGNOB TO GENERAL ELEC- TRIC COMPANY, ACORPORATION OF NEW YORK ELECTRIC HEATER Application filed Kay 11, 1929.Serial no. seam.

My invention relates to electric heaters,

section taken on the line "2-2 of Fig. 1;

more particularly to moisture-proof electric Fig. 3 is an elevationpartly-in section of a heaters, and has for its object the provision ofa simple, inexpensive and efiicient electric heater and method of makingit.-

Although obviously my invention has other applications, it isparticularly useful in connection with electric immersion heaters of thetype which comprises an encased or sheathed heating unit in which theinsulated resistance conductor is enclosed in an outer metallicprotective casing. One immersion heater of this type is described andclaimed in my Patent 1,522,992, dated January 13, 1925.

In accordance with my invention, I pro vide a metallic supporting memberfor the sheathed heating unit having a chamber which in the assembledunit serves to receive the end portion of the sheath casing and theelectrical terminal which projectstherefrom. In order to secure thesheathed unit to its support so as' to provide a mechanically strong andleak-proof connection, I wedge a body, which preferably is formed from arelatively soft metallic material such as copper between the end portionof the sheath and the surrounding walls of the chamber.

Moreover, I fill the chamber with an electrically insulating materialand cover the chamber by means of a solid insulating cloak or coverwhich is provided with an aperture for the electrical terminal.Preferably, the insulating material is inserted in the chamber in solidform andithereafter is heated to a plastic state so that when the coveris forced into place, the insulating material willcompletely fill thechamber and be forced through been secured over the mouth of thechamber,

the aperture provided in the cover so as to insulate the terminal.

I heat the insulating material further, wliere- .by it tends to expandso as to fill completely and densely the chamber vided in the cover.

'For a more complete understanding of my invention, reference should behad to the accompanying drawing in which Fig. 1 is an elevation partlyin section of an electric and aperture proheater embodying my invention;2 is a the end portions of the legs 10,10" re spec- 100- I modified formof my invention; and Fig. 4 is a section taken on the line 44 of Fig. 3.Referring to the drawing, I have shown my invention in one form inconnection with an electrical immersion heater;of the type described andclaimed in my aforementioned patent. This heater is provided with asheathed heating unit 10 and with a metallic supporting member 11for'the heating unit. 'Preferably, and as shown, 'theelectric heater isprovided with a helical coilsheathed heating unit of the type describedand claimed in my Patent No. 1,367,341, dated February 1, 1921. Briefly,this heating unit 10 comprises an outer metallic sheath 12 in which anelectrical resistance conductor 13 is embedded in acompacted mass of;powdered, heat 'refractory, electrically insulating material 14. Theinsulatin material 14 may be compacted to a hard, ense mass having goodheat conductivity in any suitable manner, as for example, by reducingthe diameter of the sheath resistance conductor 13 has its end secured Ito the electrical terminals15 and 15 which project fromthe ends of thesheath and are electrically insulated from the sheath.

The ends of the hairpin heating unit 10 are secured to the supportingmember 11 which is shown as a metallic screw plug. It will be understoodthat this screw plug .Wlll

After e Cover be screwed tightly in a suitable tapped hole in theheating receptacle so as to support the heating unit in position withinthe receptacle. The heating unit 10 thus-will be extended within thereceptacle in position to be immersed in the liquid to be heated.Moreover, the support'ing member will serve to seal theterminals againstmoisture.

As shown.-'( Fig.1) the plug 11 is provided with a pair of chambers 17,17' into which tively, of the heating unit 10 are projected.

Suitable passageways 18, 18 are provided in the bottom of the plug forreceiving the respective end portions of the legs l0, 10". It is to benoted that preferably two heating units 10 will be mounted upon the plugsupport 11. In case two units are provided, it will be understood thatthe plug will 'be provided with another pair of chambers 17 and 17 forreceiving the respective ends of the second heating unit. Moreover, itwill be understood that in case two units are used, each unit will beprovided with separate terminals and connections whereby the units maybe connected in series or in parallel relation in a well known manner soas to regulate the amount of heat produced.

As shown (Fig. 1), the end portions of the heating unit 10 will beinserted into the passageways 18, 18 so as to project somewhat beyondthe mouths of the chambers. Preferably and as shown, the lower or bottomportion of each chamber is tapered, the larger or flared end of thetapered portion merging with a straight cylindrical portion forming themouth of the chamber.

In order to secure the heating unit to the plug so as to provide aleak-proof connection, I provide abushing 20 for each chamber and forcethe bushing, which preferably is made of a suitable metallic materialsuch as soft copper, into the tapered chamber between the end portion ofthe metallic sheath and the surrounding walls of the chamber. It will beunderstood that the copper bushing may be applied to the sheath and plugin any suitable manner. Thus the bushing may be hammered into position.Preferably the straight cylindrical mouth portion of each chamber willhave a length about equal to the length of the bushing and moreover,will have a diameter of such proportions that an annular space will beformed about the projecting sheath of a size just sufficient to receivethe copper bushing. It is impossible therefore for the end of thebushing to lower as it 1s being driven into the tapered portion. Thus avery tight joint is insured. As an added proof against leaks, I furthersecure the heating unit to the plug by brazed or soldered joints 21 and21. It will be understood that if the sheath be brazed to the plug, itis desirable that the passages 18, 18*" be slightly larger at theirouter ends that the respective sheath portions pass therethro'ugh. Thusthe brazing material will be allowed to enter the enlarged portion so asto provide a more perfect brazed connection.

After the heating unit has thus been secured to the pliig, I fill thechambers 17, 17 with an electrically insulating scaling ma terial 22,this sealing material being placed in the chambers while heated to asemi-plastic state. Moreover, the insulting material will be placed overand about the projecting end portions of the metallic sheath so as toembed the outer ends of the heating unit and its terminals, thoroughlysealing the ends of the heating unit. Any suitable sealing material suchas bakelite may be used.

After the receptacles have been filled with the sealing material andthis material has been positioned around the projecting ends of thesheath, the chambers will be closed with a solid electrically insulatingcover 23 made from a suitable material, such as porcelain. As shown,this cover is sufficiently large to cover the mouths of both of thechambers and rests upon the edge of the plug surrounding the chambers.The cover 28 is hollowed so that achamber 23 is provided in the cover,this chamber together with the chamber 17, 17 in the assembled terminalserving to form'one large chamber 2A into which the ends of all of theheating units project. The cover is provided with a plurality ofapertures 25 for receiving the projecting terminals 15, 15 of theheating units. Thus if two heating units 10 be used, the cover will beprovided with four apertures, two for each heating unit. Preferably andas shown these apertures will be tapered with their larger or flaredends opening into the chamber.

It will be understood that this-insulating material 22 will be providedin sufficient quantity so that when the cover is assembled with theunit, the chamber will be entirely filled with the insulating material.It will be observed that the tapered apertures 25 are slightly largereven at their smaller ends than the terminals which they serve toreceive; By reason of this construction the plastic insulating materialwill be forced upwardly through these apertures about the terminals whenthe cover is positioned over the chambers.

After the insulating cover 23 has been assembled, suitable terminal orlead connectors 26 will be secured to the terminals 15, 15 which, ofcourse, will be projected from the cover so that the terminals may bereceived Preferably the connectors will be of the tubular type and willbe compressed upon the terminals in any suitable manner as by swaging.It will be observed that each connector at its cover end is providedwith a knife-like edge 26 so that in the assembled unit these terminalsnot only serve as lead connectors but also'serve t'o tightly close theapertures provided in the cover 23. It will be .impos-. sible thereforefor the bakelite to escape through these apertures. Moreover, theseknife edges perform a very important function in the connector assemblyoperation. It will be understood that whenthe connector is swaged on itsterminal, it has a tendency to elongate in the die and thus during thepressing opertion a heavy pressure is likely to develop between theconnector and the porcelain cover. The knife edge serves to abmaterial.

be deep as compared with the chambers prosorb any shock or blow whichotherwise might be transferred to the porcelain.

After the cover and connectors have been assembled, the insulatingmaterial 22 is treated by baking at a suitable temperature, such asapproximately 150 C. This heat treatment tends to swell or expand theinsulating It will be observed, therefore, that as a result of thiscuring operation, the large chamber 24 and the tapered apertures 25provided in the cover will be filled completely and densely with theinsulating material, so densely that it will be impossible for water ormoisture to come in contact with the terminals or ends of the heatingunit. It will be understood of course that the porcelaincover 23 willhave sufiicient mechanical strength to withstand the pressure of the insulating material.

Each connector 26 is provided with a suitable clamping member 27 whichis secured to the connector by means of a screw 28. Preferably a lockwasher 29 will be interposed between the clamping member 27 and the headof the screw.

A suitable cap or cover 30 is provided, which is secured to the plug bymeans of screws 31 and 32, and encloses the connectors and clampingmembers. An insulatin bushing 33 is provided in the cap or cover throughwhich conductors may be led to the connectors in order to connect theheater to a suit-' able source of electrical supply.

In the preferred form of my invention, shown in Figs. 3 and 4, I providethe heating unit 40 with a supporting member 41 shown as a metallicscrew plug. The supporting plug 41 will be provided with a plurality ofchambers 42, two of which will be provided for each heating unit 40.Thus if the electrical heater be provided with two heating units 40, themetallic plug 41 will be provided with four chambers, two. for eachheating unit. As shown, each chamber 42 is provided with a passageway 42for receiving the end portion of the sheath. These chambers 42 willvided in the plug 11 of Fig. 1. Thus it will be observed by reference toFig. 3 that in the assembled heater the end portions of the sheathedheating unit 40 will be projected into these chambers but will notextend completely through the chambers so as to project beyond theirmouths, as shown in Fig. 1. The electrical terminals 43, however, whichprojectfrom the ends of the sheath will bev of such length that theywill project considerably beyond the mouths of the chambers 42.

In Fig. 3 therefore eachend of each heating unit will be provided withan individual chamber. Preferably and as shown the low port. into place,the second bushing 45 will be' drical portion forming the mouth of thechamber.

- The heating unit 40 will be secured to the plug 41 in a manner similarto the method disclosed in Fig. 1. However, in this case,

two bushings '44 and 45 will be provided for each chamber 42. Thus intoeach chamber a soft metallic bushing 44 will be driven about theprojecting end portion of the heating unit between the outer walls ofthis unit and the walls of the surrounding chamber so as to I provide amechanically strong and leakproof joint. As with the chambers 17, 17' ofFig.

1, the straight cylindrical mouth portion of each chamber 42 will have alength about equal to the length of the bushing and moreover. will havea diameter of such proporti ons that the annular space formed about thesheath will be of a size just sufficient to receive the copper bushing.This construction, as has been explained, insures a very tight jointbetween the heating unit and its sup- After this bushing 44 has beenforced forced over the first bushing between the extreme outer endportion of the sheath and the surrounding walls of the tapered chamber.The heating unit 40 will be further secured to'the plug 41 by means ofthe brazed or soldered joints 46 and 46*.

Each'chamber 42 will then be provided with suitable electricallyinsulating material 47, such as bakelite. However, instead of fillin thechamber with the insulating materia while it is heated to a plasticstate, as was the case with the method described in the assembly of theheatershown in Fig. 1, the insulating material will be placed in thechamber while in a solid condition} Thus this material will be preformedsomewhat like a washer so that it will, when placed in the chamber,embrace the terminal 43 projecting from the heating unit.

After the insulating material has been placed within the chambers, theunit will be warmed slightly so as to heat the material to a plasticstate. Each chamber 42 is then closed by means of a solidelectricallyinsulating block 48 formed from a suitable insulating material, such asporcelain. As shown,-the insulating cover 48 1S provlded with anaperture 49 for the terminal 43. This cover 48 is slightlylarger thanthe mouth of the chamber which it serves to close and rests on the ledgesurrounding the mouth of the chamber so as to close the chambercompletely. Preferably a recess 50'will be provided j in the plug aboutthe mouth of each chamber to receive the cover 48 provided for thechamber. The solid cover is provided with an extension 48 on its innerside which projects downwardly into the sealing material 42. It will beunderstood, of course, that this cover 48 will be put in place while thesealing material is in its semi-plastic stateso that the material isfree to flow around the extension 48 and secure the cover uponhardening. Preferably the aperture 49 will be tapered with its larger orflared end opening into the chamber and will be larger even at itssmaller end than the terminal which it serves to receive. It will beunderstood therefore that when the cover is forced into the softinsulating material that the material will flow upwardly through thetapered aperture about the-terminal.

A connector 51 will then be secured to the end of each terminal.Preferably these connectors will be of the tubular type and will becompressed about the projecting ends of the terminals in some suitablemanner as by swaging. It will be observed that each connector isprovided with a knife edge 51 at its cover end so as to closeetfectively the open end of the aperture provided in the cover, and toprevent injury to the cover during the assembly of the connector. Eachconnector. will be provided with a clamping member 52 secured to theconnector by means of a screw 53.

As before, the heater will then be baked at a suitable temperature, suchas 150 C., in order to cure the insulatin compound. As described, thisprocess tends to expand the insulating compound so as to fill completelyand densely the chambers 42 and the tapered apertures provided in thecover members 48. In order to insure that there will be no leakage ofbakelite during the heating or baking operation, I provide a suitablewasher 54 for each cover -18. Preferably a dish-shaped copper washerwill be provided. In the assembly of the heater, the washer will beinserted under the head of the porcelain insulating cover with its smalldiameter against the head of the cover. It will be observed thereforethat when the cover is forced into position over the chamber, the washerwill be flattened out so that its outer or larger diameter will beforced against the walls of the recess while its smaller diameter willbe forced against the relativel irregular surface of the porcelaincover. reason of this construction a very tight joint is-efiected.

- A suitable cap or cover 55 is provided which is secured to the plug bymeans of screws 56 and 57, and encloses theconnectors-and clampingmembers. This cover is provided with an insulating bushing 58 throughwhich conductors may bepassed tothe connectors in order to connect theheater to a suitable source of electrical supply.

-What I claim as new and. desire to secure by Letters Patent of theUnited States, is:

1. An electric heater comprising a metallic sheath from which anelectrical terminal projects, a support for said metallic sheath,

said support being provided with a chamber into which the end portion ofsaid sheath is projected, means for securing said sheath to said supportcomprising a metallic member wedged about the projecting end portion ofsaid sheath between said portion and the surrounding walls of saidchamber, and insulating sealing means in said chamber about the end ofsaid sheath and said projecting terminal.

2. An electric heater comprising a metallic sheath from which anelectrical terminal projects, a support for said sheath, said supportbeing provided with a chamber and a passageway through which the endportion of said sheath is extended so as to project into said chamber,means for securing said sheath to said receptacle comprising a metallicmember surrounding the projecting end portion of said sheath and wedgedtight- 1y between said projecting end portion and the adjacent walls ofsaid chamber, an insulating sealing material in said chamber embeddingthe projecting end portion of said sheath and said terminal and a blockof insulating material closing said chamber providedwitli an aperturefor said terminal.

3.- An electric immersion heater comprising a metallic sheath from whichan electric'al terminal projects, a support for said sheath, saidsupport being provided with a chamber and a passageway through which theend portion of said sheath is extended so as to project into saidchamber, means for securing said sheath to said receptacle so as to forma water-tight connection therewith comprising a metallic: membersurrounding v the projecting end portion of said sheath and wedgedtightly between said projecting end portion and the her, an insulatingsealing material in said chamber embedding the projecting end portion ofsaid sheath and said terminal, a block of insulating material closingsaid chamber provided with an aperture for said terminal, a resistanceconductor in said sheath electrically connected with said terminal andpowdered heat refractory insulating material compacted in said sheatharound said resistance conductor so as to conduct heat freely from saidresistance conductor to said sheath.

4. An electric heater comprising a metallic sheath from which anelectrical terminal pro- 'ects, a support for said sheath, said supporting provided with a chamber and a passageway through which the endportion of' said sheath is extended so as to project into said chamber,means for securing said sheath 1'.)

to said support comprisinga metallic memadjacent walls of said chambersurrounding the projecting end portion r of said sheath and wedgedtightly between said projecting end portion and the adjacent wallsof'said chamber, an insulating sealing in material in said chamberembedding the projecting-endsportion of said sheath and said terminal, ablock of insulating material covering said. chamber and projecting intosaid insulating material, said block having an aperture for saidterminal, and a lead connector secured to the end of said terminal so asto secure said cover and close the aperture extending therethrough.

5. An electric immersion heater comprising a metallic sheath having itsends adjacent each other and from which electrical terminals project, asupport for said sheath pro- ,vided with a pair of chambers into whichthe respective end portions of said sheath are projected, means forsecuring said sheath to said support comprising a pair of metallicbushings, one for each chamber, each metallic bushing surrounding theend portion of the sheath projecting into its chamber and being wedgedtightly between the sheath and the surrounding walls of the chamber, aninsulating sealing material in each chamber embedding the end of thesheath within the chamber and the terminal projecting from said sheath,a pair of insulating covers, one for each chamber, each cover projectinginto the insulating material within its chamber and provided with anaperture for the terminal, and a pair of connectors,one for eachterminal, said connectors serving both to secure said covers and toclose the apertures extending therethrough.

6. The method of making a moisture-proof electric heater having ametallic sheath, an

electrical terminal projecting from said sheath and a support for saidsheath which comprises forming a chamber in said support and apassageway for the chamber leading from the chamber to the exterior ofsaid support, inserting the end of said sheath through said passagewayso that the end portion thereof projects into said chamber, securingsaid sheath to said support, inserting aebody of solid insulatingmaterial within said chamber, warming said insulating material to aplastic state, providing a cover for said chamber formed with anaperture therethrough for receiving said projecting terminal, securingsaid cover over the mouth of said chamber and then heating said unitwhereby the insulating material tends to expand so as to fill completelyand densely the" chamber and aperture extending through said cover.

7. The method of making an electric immersion heater provided with ametallic sheath having its ends adjacent eachother, an electricalterminal projecting from each end of said sheath and a metallic supportfor said chambers, respectively, wedgmg a metallie bushing between eachprojectm end por-- tion of the sheath andthe surroundingwalls taperedaperture, compressing a tubular lead connector member about eachterminal so as to secure the covers and close their apertures and thenheating said unit whereby the insulating material tends to expand so asto fill completely and densely the chambers and aperture provided intheir covers.

In witness whereof I have hereunto set my hand this 14th day of May,1929.

-- CHARLES C. ABBOTT.

